Increase in dopamine and DOPAC levels in noradrenergic terminals after electrical stimulation of the ascending noradrenergic pathways.

The effect of electrical stimulation of the ascending noradrenergic neurons on the formation of dopamine and its major deaminated metabolite dihydroxyphenylacetic acid (DOPAC) in the hippocampal formation, a predominantly noradrenaline-rich brain area, has been investigated in the rat. Electrical stimulation of the locus coeruleus or ascending noradrenergic pathways caused a pronounced increase in hippocampal dopamine and DOPAC levels which paralleled the increase in free and conjugated dihydroxyphenylethyleneglycol levels. The elevation of hippocampal DOPAC was no longer seen after chemical lesion of the noradrenergic pathways. It is suggested that the enhanced formation of dopamine and DOPAC in hopocampal noradrenergic terminals under conditions of increased noradrenergic impulse flow may be connected to an inefficient beta-hydroxylation of dopamine to noradrenaline with a subsequent oxidative deamination of dopamine into its degradation products.